Process and plant for producing tyres for vehicle wheels

ABSTRACT

A process and a plant for producing tyres for vehicle wheels are described. Building of a crown structure of the tyre includes building a crossed belt structure on a substantially cylindrical first forming drum, transferring the crossed belt structure from the first forming drum to an annular holding member, positioning a second forming drum in a radially inner position with respect to the annular holding member, transferring the crossed belt structure from the annular holding member to the second forming drum by radially expanding the second forming drum until it is brought into contact with the crossed belt structure so as to toroidally shape the crossed belt structure, and depositing at least one zero degrees belt layer on the second forming drum in a radially outer position with respect to the toroidally-shaped crossed belt structure.

The present invention relates to a process and a plant for producing tyres for vehicle wheels.

A tyre for vehicle wheels generally comprises a carcass structure, a crown structure arranged in radially outer position with respect to the carcass structure and a pair of sidewalls that are the axially outer surfaces of the tyre, with respect to a mid-plane perpendicular to the rotation axis of the same tyre.

The carcass structure comprises at least one carcass ply formed of reinforcing cords incorporated in a matrix of elastomeric material. The carcass ply has opposite end edges respectively engaged with annular anchoring structures. The latter are arranged in the areas of the tyre usually identified by the name “beads” and each of them is usually formed of a substantially circumferential annular insert, or “bead core”, on which at least one filling insert is applied, in a radially outer position, the latter being radially tapered moving away from the rotation axis.

Specific reinforcing inserts having the function of improving the transmission of torque to the tyre can be provided at the beads.

In the case of “tubeless” tyres, i.e. without air chamber, a layer of elastomeric material, generally known as “liner”, can also be provided in a radially inner position with respect to the carcass structure to provide the necessary impermeability to the inflation air of the tyre. Generally, the liner extends from one bead to the other.

The crown structure comprises a belt structure and, in a radially outer position with respect to the belt structure, a tread band made of elastomeric material.

The belt structure comprises a belt layer, or more belt layers arranged in radial juxtaposition with respect to one another, comprising reinforcing cords having an orientation substantially parallel to the direction of circumferential extension of the tyre (zero degrees belt layer) or, in the case of more belt layers, a crossed orientation. In this last case, said zero degrees belt layer can be provided in a radially outer position with respect to the belt layers having a crossed orientation.

Longitudinal and transversal grooves are typically formed on the tread band and they are arranged to define a desired tread pattern. Between the tread band and the belt structure a so-called “under-layer of the tread band” can be arranged, made of an elastomeric material having suitable properties for obtaining a stable union of the belt structure with the tread band itself.

The sidewalls are made of elastomeric material and define the axially outer surfaces of the tyre, i.e. the surfaces arranged in the axially outermost position with respect to the annular anchoring structures, the carcass ply(ies), the belt layer(s) and possibly at least one portion of tread band. For example, each sidewall extends from one of the lateral edges of the tread band up to the respective bead annular anchoring structure.

Throughout this description and in the claims, any numerical value is deemed to be preceded by the term “about” to also indicate any numerical value that differs slightly from the one indicated, for example to take into account the dimensional tolerances typical of the field of reference.

The term “elastomeric material” is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Such a composition can also comprise additives like, for example, a cross-linking agent and/or a plasticizer. Thanks to the presence of the cross-linking agent, such a material can be cross-linked by heating, so as to form the final manufactured product.

The term “green tyre” is used to indicate a tyre obtained from the building process and not yet molded and vulcanized.

The term “finished tyre” is used to indicate a tyre obtained by subjecting a green tyre to a molding and vulcanization process.

The term “tyre” is used to indicate a finished tyre or a green tyre.

The terms “axial”, “axially”, “radial”, “radially”, “circumferential” and “circumferentially” are used with reference to the tyre or to a forming drum used in the production process of the tyre.

In particular, the terms “axial” and “axially” are used to indicate references/parameters arranged/measured or extending in a direction substantially parallel to the rotation axis of the tyre or of the forming drum.

The terms “radial” and “radially” are used to indicate references/parameters arranged/measured or extending in a direction substantially perpendicular to the rotation axis of the tyre or of the forming drum and lying in a plane comprising such a rotation axis.

The terms “circumferential” and “circumferentially” are used to indicate references/parameters arranged/measured or extending along a circumference that extends around the rotation axis of the tyre or of the forming drum.

The term “structural component” of a tyre is used to indicate any portion of the tyre capable of performing its function or a part thereof. Examples of structural components of the tyre are the following components: the carcass structure, the crown structure, or parts thereof, like liner, under-liner, anti-abrasion inserts, bead core, filling inserts in the area of the bead (and therefore the annular anchoring structures defined by bead cores and respective filling inserts), carcass ply(ies), belt layer(s), belt under-layer, under-layer of the tread band, sidewalls, sidewall inserts, tread band, reinforcing inserts made of textile or metallic material, reinforcing inserts made of elastomeric material etc., or a part thereof.

The term “crossed belt structure” is used to indicate a belt structure comprising at least two belt layers arranged in radial juxtaposition over one another and each including a plurality of textile and/or metallic and/or hybrid parallel reinforcing cords, tilted with respect to the direction of circumferential extension of the tyre (and therefore to an axial mid-plane of the tyre), wherein the reinforcing cords of one belt layer are tilted with respect to said axial mid-plane of the tyre by the same angle and on the opposite side to the reinforcing cords of another belt layer.

The term “belt assembly” is used to indicate an annular assembly comprising a crossed belt structure and a zero degrees belt layer arranged in a radially outer position with respect to the crossed belt structure.

The term “cylindrical shaping” of a belt assembly is used to indicate a building cycle aimed at obtaining a belt assembly having a substantially cylindrical shape.

The term “toroidal shaping” of a belt assembly is used to indicate a building cycle aimed at obtaining a belt assembly having a substantially toroidal shape and a profile in a radial section close to the profile in a radial section of the corresponding finished tyre.

The term “substantially toroidal forming drum” is used to indicate a forming drum the outer surface of which has a profile in a radial section such that, whatever semi-finished product is deposited thereon during the building of a tyre being processed, the semi-finished product takes a shape close to the shape taken in the finished tyre.

The term “tyre being processed” is used to indicate a tyre at any stage of the relative production process that goes from building at least one structural component up to obtaining the finished tyre. For example, a tyre being processed is the one which exits from the working station dedicated to building the belt assembly to proceed towards the working stations dedicated to the deposition on the belt assembly of the possible under-layer of the tread band, of possible reinforcing inserts and of the tread band itself.

The term “functionally independent” is used to indicate the capability of a member or device to perform the function it is provided for in an autonomous manner, i.e. without interacting or cooperating with other members or devices which are provided to perform the same function.

The term “normal operation” is used to indicate the normal operating conditions of a tyre production plant, thus excluding possible starting or stopping transient periods of the plant itself, for example linked to a change of production batch.

The term “cycle time of a building device” is used to indicate the time that elapses between the exit of a tyre being processed from the building device and the exit of the next tyre being processed from the same building device, in normal operating conditions. The cycle time of a building device is therefore given by the sum of the time necessary to load the tyre being processed in the building device, of the time necessary to carry out the building activity, and of the time necessary to unload the tyre being processed from the building device.

The term “total cycle time of a building plant” is used to indicate the time that elapses between the exit of a tyre being processed from the building plant and the exit of the next tyre from the same building plant, in normal operating conditions.

The term “downstream”/“head” and “upstream”/“tail” are used with reference to a direction of movement. Therefore, assuming for example a direction of movement from left to right, a “downstream” or “head” position with respect to any reference element indicates a position to the right of said reference element and an “upstream” or “tail” position indicates a position to the left of said reference element.

The production cycles of a tyre provide that, after a building process of a green tyre in which the various structural components of the tyre itself are built and assembled, the green tyres are transferred to a molding and vulcanization line wherein a molding and vulcanization process adapted to define the structure of the finished tyre according to a desired geometry and tread pattern is carried out.

The building of the structural components of the tyres and the subsequent assembly thereof is carried out on suitable forming drums. For example, the carcass structure can be built on a first forming drum, known as first stage drum, and the crown structure can be built on a second forming drum, known as auxiliary or second stage drum. The assembly of the carcass structure to the crown structure can be carried out on the first forming drum, in which case the first stage drum takes the name of single stage or “unistage” drum, or on a different forming drum, known as shaping drum.

An example of a plant for producing green tyres is described in WO2010/070374. Such a plant comprises:

-   -   at least one building line for building the carcass structure on         a first forming drum, such a building line comprising a         plurality of working stations arranged according to a sequential         series;     -   at least one building line for building the crown structure on         at least one second forming drum, such a building line         comprising a plurality of working stations arranged according to         a sequential series; and     -   at least one shaping and assembling station of the tyre being         processed adapted to shape the carcass structure on the first         forming drum by assembling it to the crown structure of the tyre         being processed.

Examples of first and/or second stage forming drums which can be used in a tyre production process like the one described in the aforementioned WO2010/070374 are described in WO2008/152453 and US2012/0318460. In both cases they are radially contractable/expandable forming drums having a substantially cylindrical shape.

The forming drums described in the cited documents are widely used in the production cycles of tyres in which a cylindrical shaping of the belt assemblies is carried out.

The Applicant has observed that, for example in the production cycles of racing or high-performance tyres, it is necessary to be able to adequately control the deformations to which the green tyre is subjected during the molding and vulcanization process, in order to provide the tyre with the desired reactivity and driving precision. In order to be able to do this, it is advisable, before actuating the molding and vulcanization process, to provide for a toroidal shaping such as to give the belt assembly a substantially toroidal shape that is as close as possible to the shape of the finished tyre.

A way to carry out a toroidal shaping of the belt assembly would consist in building the belt assembly on a substantially toroidal forming drum. According to the Applicant, however, it would be extremely difficult to be able to automatically (i.e. not manually) join the end portions of the belt layers of the crossed belt structure if such belt layers (each of which being defined by a semi-finished product shaped like a substantially flat strip cut to size) are deposited on a substantially toroidal forming drum.

The Applicant has thus considered that it is preferable to identify an alternative solution that provides for building the crossed belt structure on a substantially cylindrical forming drum, therefore as in the case of cylindrical shaping of the belt assemblies, using a substantially toroidal forming drum only for the subsequent deposition of the zero degrees belt layer. Indeed, this last operation can be carried out on a forming drum having any shape, even toroidal, as no joins need to be made.

The Applicant has therefore sought for a solution suitable for actuating a toroidal shaping of the belt assemblies that, in a first part of the building cycle of the belt assembly, in particular in the part of the cycle dedicated to building the crossed belt structure, provides for the use of a substantially cylindrical forming drum and in a second part of the building cycle of the belt assembly, in particular in the part of cycle dedicated to the deposition of the zero degrees belt layer on the crossed belt structure, provides for the use of a substantially toroidal forming drum.

With the aim of making a technologically and operatively flexible production plant, so as to reduce the manufacturing costs of the plant and of the devices and apparatuses thereof and the spaces occupied by such devices and apparatuses, the Applicant has considered that it would be advisable for the aforementioned solution to also allow the actuation of a cylindrical shaping of the belt assemblies when desired.

The Applicant has realised that it is possible to provide for a building cycle of the belt assembly having a first part of cycle, dedicated to building the crossed belt structure, in which a forming drum of substantially cylindrical shape is used both when a cylindrical shaping of the belt assemblies has to be carried out and a toroidal shaping of the belt assemblies has to be carried out and a second part of cycle, dedicated to the deposition of the zero degrees belt layer, in which when a cylindrical shaping of the belt assemblies has to be carried out the aforementioned substantially cylindrical forming drum continues to be used, whereas when a toroidal shaping of the belt assemblies has to be carried out, the crossed belt structure deposited on the substantially cylindrical forming drum is transferred to a substantially toroidal forming drum for the subsequent deposition of the zero degrees belt layer on such a substantially toroidal forming drum.

The Applicant has perceived that an effective way to carry out the transfer of the crossed belt structure from the substantially cylindrical forming drum to the substantially toroidal forming drum when a toroidal shaping of the belt assemblies has to be carried out is that of transferring the crossed belt structure from the substantially cylindrical forming drum to an annular holding member configured to pick up the crossed belt structure from the substantially cylindrical forming drum when the latter is at said annular holding member, hold it until the substantially toroidal forming drum arrives at the annular holding member to then transfer it to the substantially toroidal forming drum, such an annular holding member being bypassed when, on the other hand, a cylindrical shaping has to be carried out (in which case the substantially toroidal forming drum is not used).

The Applicant has thus found that by transferring to an annular holding member a crossed belt structure built on a substantially cylindrical forming drum, then transferring said crossed belt structure from the annular holding member to a substantially toroidal forming drum and subsequently depositing a zero degrees belt layer on said substantially toroidal forming drum in a radially outer position with respect to the crossed belt structure it is possible to carry out a toroidal shaping of a belt assembly automatically by a building device of the belt assembly that is also capable of actuating a cylindrical shaping.

The present invention therefore relates, in a first aspect thereof, to a process for producing tyres for vehicle wheels.

Preferably, it is provided that a crown structure of the tyre is built.

Preferably, the building of the crown structure comprises building a crossed belt structure on a substantially cylindrical first forming drum.

Preferably, the building of the crown structure comprises transferring said crossed belt structure from the first forming drum to an annular holding member.

Preferably, the building of the crown structure comprises positioning a radially contractable/expandable second forming drum in a radially inner position with respect to said annular holding member.

Preferably, the building of the crown structure comprises transferring the crossed belt structure from said annular holding member to the second forming drum.

Preferably, such a transfer is carried out by radially expanding the second forming drum until it is brought into an expanded condition in which it is in contact with the crossed belt structure so as to toroidally shape said crossed belt structure.

Preferably, the building of the crown structure comprises depositing at least one zero degrees belt layer on the second forming drum in a radially outer position with respect to the toroidally-shaped crossed belt structure.

The Applicant believes that thanks to the fact that the crossed belt structure is deposited on a substantially cylindrical forming drum and the zero degrees belt layer is deposited on the crossed belt structure after the latter has been transferred from the substantially cylindrical forming drum to the substantially toroidal forming drum by said annular holding member it is possible to automatically (i.e. not manually) join the end portions of the belt layers of the crossed belt structure also when a toroidal shaping of the belt assembly has to be carried out.

In a second aspect thereof, the invention relates to a plant for producing tyres for vehicle wheels.

Preferably, a crown structure building line is provided.

Preferably, a belt assembly building device is provided in said crown structure building line.

Preferably, a trolley is provided in said crown structure building line, the trolley being moveable along a first direction of movement.

Preferably, a substantially cylindrical first forming drum is provided in said crown structure building line, the first forming drum being configured to be coupled with said trolley.

Preferably, a second forming drum is provided in said crown structure building line, the second forming drum being configured to take a substantially toroidal shaping.

Preferably, said second forming drum is configured to be coupled to said trolley.

Preferably, the second forming drum is radially contractable/expandable.

Preferably, a first working area is provided.

Preferably, said first working area comprises a crossed belt structure building device.

Preferably, a second working area is provided in said crown structure building line.

Preferably, said second working area is arranged downstream of said first working area with reference to said first direction of movement.

Preferably, said second working area comprises a deposition device configured to deposit at least one zero degrees belt layer in a radially outer position with respect to said crossed belt structure.

Preferably, a first service area is provided in said crown structure building line.

Preferably, said first service area is arranged downstream of said second working area with reference to said first direction of movement.

Preferably, said first service area comprises an annular holding member.

Preferably, a second service area is provided in said crown structure building line.

Preferably, said second service area is arranged downstream of said first service area with reference to said first direction of movement.

The Applicant believes that a plant of the type described above is suitable for actuating both a cylindrical shaping of the belt assembly and a toroidal shaping of the belt assembly, like for example the configuration which can be obtained with the process discussed with reference to the first aspect of the invention. In particular, the Applicant believes that the actuation of a toroidal shaping of the belt assembly can be obtained thanks to the provision of service areas (the aforementioned first service area and second service area) in which the crossed belt structure built on the substantially cylindrical forming drum supported by the trolley is transferred to the annular holding member and the substantially cylindrical forming drum, without the crossed belt structure thereon, is released by the trolley so that the latter can pick up the substantially toroidal forming drum and bring it in a radially inner position with respect to the annular holding member. At this point, the crossed belt structure can be transferred from the annular holding member to the substantially toroidal forming drum and it is then possible to carry out the deposition of the zero degrees belt layer on the substantially toroidal forming drum in a radially outer position with respect to the crossed belt structure, thus obtaining the desired toroidal shaping of the belt assembly.

In at least one of the aforementioned aspects, the present invention can have at least one of the preferred features described hereinafter.

Preferably, said second forming drum is substantially toroidal.

Preferably, the first forming drum is moveable from a first working area to said second service area along said first direction of movement. Such a movement is carried out both when a cylindrical shaping of the belt assembly has to be carried out and when a toroidal shaping of the belt assembly has to be carried out.

Preferably, it is provided that the first forming drum is arranged at least in said first working area to carry out the building of the crossed belt structure on the first forming drum. Such a provision is also actuated both when a cylindrical shaping of the belt assembly is carried out and when a toroidal shaping of the belt assembly is carried out.

Once the crossed belt structure has been built on the first forming drum different provisions are foreseen depending on whether a cylindrical shaping of the belt assembly or a toroidal shaping of the belt assembly has to be carried out.

Preferably, when a cylindrical shaping of the belt assembly has to be carried out, it is provided that the first forming drum is moved along said first direction of movement and stops in the second working area to carry out the deposition of the zero degrees belt layer in a radially outer position with respect to the crossed belt structure.

More preferably, it is provided that the first forming drum also stops in the second service area to be picked up by a drum transfer device in order to deposit on the first forming drum the tread band and possible other structural components of the tyre, like for example the under-layer of the tread band and/or possible reinforcing inserts. In this case, the first forming drum is not stopped in the first service area.

When, on the other hand, a toroidal shaping of the belt assembly has to be carried out, it is provided that the first forming drum stops at least in said first service area. During such a stop it is possible to carry out the transferal of the crossed belt structure from the first forming drum to the annular holding member.

Preferably, it is provided that the first forming drum without the crossed belt structure thereon stops at least in said second service area. It is also provided that the first forming drum is held in the second service area while the belt assembly is built on the second forming drum.

Preferably, the second forming drum is moveable from said second service area to said second working area along a second direction of movement opposite to said first direction of movement. Such a movement therefore occurs along a path in part identical to the path of the first forming drum, with a consequent optimization of the spaces.

Preferably, it is provided that the second forming drum stops at least in said first service area in a radially inner position with respect to the annular holding member. During such a stop it is possible to carry out the transfer of the crossed belt structure from the annular holding member to the second forming drum upon radially expanding the second forming drum.

Preferably, the second forming drum is moveable along said first direction of movement from said second working area to said second service area, from which it can be picked up to be brought to other devices and/or apparatuses of the crown structure building line, like for example the devices configured to apply the tread band, possible devices configured to apply the possible under-layer of the tread band and possible devices configured to apply possible reinforcing inserts.

Preferably, it is provided that at least one belt layer is deposited on the first forming drum when it the latter in said first working area.

More preferably, it is provided that two belt layers are deposited.

In this case, preferably, the first forming drum is at first arranged in a first operative station defined in said first working area.

Preferably, in said first operative station a first belt layer is deposited on the first forming drum.

Preferably, the first forming drum is subsequently moved from said first operative station to a second operative station defined in said first working area.

Preferably, said second operative station is arranged downstream of said first operative station with reference to said first direction of movement.

Preferably, in said second operative station a second belt layer is deposited on the first forming drum in a radially outer position with respect to said first belt layer.

In this way it is possible to build a crossed belt structure on the first forming drum.

Preferably, it is provided that the first forming drum is moved along said first direction of movement from said first working area to a first service area arranged downstream of said first working area with reference to said first direction of movement.

Preferably, said first service area comprises said annular holding member.

Preferably, the first forming drum is arranged in a radially inner position with respect to the annular holding member.

Preferably, the first forming drum is radially contractable/expandable.

Preferably, the annular holding member is radially contractable/expandable.

Preferably, after having arranged the first forming drum in a radially inner position with respect to the annular holding member, the annular holding member is radially contracted until it is brought into contact with the crossed belt structure arranged on the first forming drum.

Preferably, after the radial contraction of the annular holding member a radial contraction of the first forming drum is carried out, leaving the crossed belt structure associated with the annular holding member.

Thanks to such provisions the crossed belt structure is transferred from the substantially cylindrical forming drum to the annular holding member.

Preferably, it is provided that the first forming drum is moved, without the crossed belt structure thereon, along said first direction of movement from said first service area to a second service area arranged downstream of said first service area with reference to said first direction of movement.

Preferably, said second service area comprises a first support member.

Preferably, it is provided that the first forming drum is transferred to the first support member.

More preferably, the first forming drum is held by the first support member while the belt assembly is built on the second forming drum.

In preferred embodiments, the first support member is moveable in said second service area between a first loading/unloading position and a waiting position.

Preferably, the transfer of the first forming drum to the first support member is carried out when the first support member is in said first loading/unloading position.

In this way, when the first support member brings the first forming drum in the waiting position the second forming drum can be arranged in the loading/unloading position to be picked up and to proceed with the building of the belt assembly thereon.

Preferably, the second forming drum is moveable from said second service area to said first service area along a second direction of movement opposite to said first direction of movement. Such a movement allows the second forming drum to be arranged in a radially inner position with respect to the annular holding member.

In preferred embodiments, said second service area comprises a second support member. Such a support member is configured to support the second forming drum before the latter is moved from said second service area to said first service area.

Preferably, the second support member is moveable in said second service area between a second loading/unloading position and a third loading/unloading position.

Preferably, before moving the second forming drum from said second service area to said first service area the second support member is moved from said second loading/unloading position to said third loading/unloading position.

In preferred embodiments, moving the first forming drum between said first loading/unloading position and said waiting position is carried out simultaneously with moving the second forming drum between said second loading/unloading position and said third loading/unloading position. In this way, an advantageous reduction of the cycle time of the building device of the belt assembly is obtained.

Preferably, said third loading/unloading position coincides with said first loading/unloading position and said waiting position coincides with said second loading/unloading position. In this way, an advantageous reduction of the dimensions in plan of the second service area is obtained.

Preferably, the first support member and the second support member are associated with a single manipulator irremovably arranged in said second service area. This makes it possible to further reduce the dimensions in plan of the second service area.

Preferably, after having transferred the crossed belt structure from the annular holding member to the second forming drum in said first service area, the second forming drum is moved along said second direction of movement from said first service area to a second working area arranged between said first working area and said first service area. In such a second working area at least one zero degrees belt layer is deposited on the substantially toroidal forming drum, in a radially outer position with respect to the crossed belt structure, thus obtaining the desired toroidal shaping of the belt assembly.

Preferably, after having deposited said at least one zero degrees belt layer on the second forming drum, the second forming drum is moved from said second working area to said second service area along said first direction of movement.

More preferably, the second forming drum is transferred to the second support member arranged in the second service area.

Preferably, after having transferred said second forming drum to said second support member the first forming drum is transferred from said second service area to said first working area along said second direction of movement. At this point it is possible to proceed with a new building cycle of a belt assembly. Such a building cycle can be aimed at actuating a cylindrical shaping of the belt assembly or at actuating a toroidal shaping of the belt assembly.

Preferably, it is provided that after having transferred the second forming drum to said second support member the second forming drum is picked up from the second support member by a drum transfer device.

Preferably, a third substantially toroidal forming drum is associated with the second support member. At this point it is possible to proceed with a new building cycle of a belt assembly aimed at the actuation of a toroidal shaping of the belt assembly.

Preferably, said first working area can be arranged downstream of a starting position of said trolley with reference to said first direction of movement.

Preferably, in order to build the crossed belt structure a first deposition apparatus configured to build a first belt layer is provided.

Preferably, said first deposition apparatus is arranged in a first operative station defined in said first working area.

Preferably, a second deposition apparatus configured to build a second belt layer is provided.

Preferably, said second deposition apparatus is arranged in a second operative station defined in said first working area.

Preferably, said second operative station is arranged downstream of said first operative station with reference to said first direction of movement.

In preferred embodiments, the first forming drum is radially contractable/expandable.

In the aforementioned preferred embodiments or in further preferred embodiments, the annular holding member is radially contractable/expandable.

In the aforementioned preferred embodiments or in further preferred embodiments, said second service area comprises a first support member configured to support said first forming drum.

In the aforementioned preferred embodiments or in further preferred embodiments, said second service area comprises a second support member configured to support said second forming drum.

In the aforementioned preferred embodiments or in further preferred embodiments, said first support member and said second support member are associated with a single manipulator irremovably arranged in said second service area.

Preferably, said manipulator is a rotating manipulator with an oblique rotation axis.

Preferably, the movement of the first forming drum along said first direction of movement occurs by a trolley.

Preferably, the movement of the first forming drum along said second direction of movement occurs by the aforementioned trolley.

Preferably, said first forming drum is moveable by said trolley from said second service area to said first working area along said second direction of movement passing in a radially inner position with respect to said annular holding member.

Preferably, during the aforementioned movement said first forming drum is not stopped in said first service area.

Preferably, during the aforementioned movement said first forming drum is not stopped in said second working area.

Preferably, the movement of the second forming drum along said first direction of movement occurs by a trolley.

Preferably, the movement of the second forming drum along said second direction of movement occurs by the aforementioned trolley.

Preferably, the movement of the second forming drum along said first direction of movement and/or along said second direction of movement occurs by the same trolley that moves the first forming drum along said first direction of movement and/or along said second direction of movement.

Preferably, said second forming drum is moveable from said second working area to said second service area along said first direction of movement passing in a radially inner position with respect to said annular holding member.

In preferred embodiments, a plurality of substantially toroidal forming drums enter into, and exit from, said belt assembly building device in succession while the first forming drum always remains inside said building device. In the case of toroidal shaping of the belt assembly the first forming drum is thus a service drum used only for building the crossed belt structure inside the aforementioned building device.

Preferably, in the case of toroidal shaping of the belt assembly the building of the crown structure comprises the deposition of a tread band on the second forming drum in a radially outer position with respect to said at least one zero degrees belt layer, whereas in the case of cylindrical shaping of the belt assembly the building of the crown structure comprises the deposition of the tread band on the first forming drum in a radially outer position with respect to said at least one zero degrees belt layer.

Preferably, the deposition of the tread band is carried out by a suitable deposition device arranged downstream of said second service area with reference to said first direction of movement. This is the case both when a toroidal shaping of the belt assembly is carried out and when a cylindrical shaping of the belt assembly is carried out.

Further features and advantages of the present invention will become clearer from the following detailed description of a preferred embodiment thereof, made with reference to the attached drawings.

In such drawings:

FIG. 1 is a schematic radial half-section view of a tyre that can be made by the process and the plant of the invention;

FIG. 2 is a schematic top view of a plant for producing tyres for vehicle wheels according to an embodiment of the invention;

FIGS. 3-17 are schematic top views of a belt assembly building line of the plant of FIG. 2 in various operative configurations thereof taken during the process of the invention;

FIG. 18 is a schematic front view of an annular holding member provided in the building line of FIGS. 3-17 ;

FIGS. 19-20 are schematic perspective views of a manipulator provided in the building line of FIGS. 3-17 , in two different operative configurations thereof.

In FIG. 1 , an example of a tyre that can be produced in a plant for producing tyres for vehicle wheels in accordance with the present invention is indicated with reference numeral 2. Such a tyre can be produced by carrying out the process of the present invention.

The tyre 2 has a mid-plane A perpendicular to the rotation axis R thereof (in FIG. 2 the position of the rotation axis R with respect to the section of the tyre 2 is shown in an indicative and schematic manner). The mid-plane A divides the tyre 2 into a first axial half 2 a and a second axial half. For the sake of simplicity of illustration, FIG. 2 shows only the first axial half 2 a of the tyre 2, the other half being substantially a mirror image of the first axial half 2 a (except for the tread pattern that may not be symmetrical with respect to the aforementioned mid-plane A).

The tyre 2 substantially comprises a carcass structure 3 having one or two carcass plies 4 a, 4 b. A layer of impermeable elastomeric material or so-called liner 5 is applied in a radially inner position with respect to the carcass ply(ies) 4 a, 4 b.

Two annular anchoring structures 6 (only the one of the axial half 2 a is shown in FIG. 2 ) are engaged, in axially opposite positions (with respect to the mid-plane A), to respective end edges of the carcass ply(ies) 4 a, 4 b. Each of the two annular anchoring structures 6 comprises a so-called bead core 6 a carrying, in a radially outer position, an elastomeric filler 6 b. The two annular anchoring structures 6 are integrated close to areas usually identified with the name of “beads” 7 (only the one of the axial half 2 a of which is shown in FIG. 2 ), at which the engagement between the tyre 2 and a respective mounting rim usually occurs.

A crown structure 9′ is arranged in a radially outer position with respect to the carcass structure 3, the crown structure 9′ comprising a belt assembly 8′ and a tread band 9 arranged in a radially outer position with respect to the belt assembly 8′.

The belt assembly 8′ comprises a crossed belt structure 8 comprising two radially juxtaposed belt layers 8 a, 8 b, and a zero degrees belt layer 8 c arranged in a radially outer position with respect to the crossed belt structure 8.

The crossed belt structure 8 can be associated with so-called “under-belt inserts” 10, each arranged between the carcass ply(ies) 4 a, 4 b and one of the axially opposite end edges of the crossed belt structure 8.

Two sidewalls 11, each extending from the corresponding bead 7 to a corresponding lateral edge of the tread band 9, are applied in axially opposite positions (with respect to the mid-plane A) on the carcass ply(ies) 4 a, 4 b. The assembly of the portion of each sidewall 11 close to the respective lateral edge of the tread band 9 and of each portion of the tread band 9 close to the respective sidewall 11 is known as shoulder 12 of the tyre 2.

FIG. 2 shows a plant 1 for producing tyres 2 for vehicle wheels according to an embodiment of the invention.

The plant 1 comprises a carcass structures building line 100, a crown structures building line 200, a shaping and assembling machine 300 for obtaining a green tyre 2′ and a molding and vulcanization station 400 for obtaining the finished tyre 2.

In a normal operation of the plant 1, the carcass structures building line 100 comprises a plurality of working stations (like for example the one indicated below with reference numeral 125) comprising respective building devices configured to build a plurality of carcass structures on respective forming drums 110 picked up from a first drum storage area 111.

Similarly, the crown structures building line 200 comprises a plurality of working stations (like for example the one illustrated in FIGS. 3-17 ) comprising respective building devices configured to build a plurality of crown structures on respective forming drums 210 picked up from a second drum storage area 211.

Preferably, the forming drums 110 are substantially cylindrical.

Instead, as to the forming drums 210, they are substantially cylindrical in the case in which a cylindrical shaping of the belt assembly has to be carried out or substantially toroidal in the case in which a toroidal shaping of the belt assembly has to be carried out.

Hereinafter, reference will always be made to forming drums 210 having a substantially toroidal shape, unless when expressly stated otherwise.

The carcass structures building line 100 comprises a first path 120 comprising building devices configured to deposit on the forming drum 110 a first part of structural components of the carcass structure.

The first path 120 of the carcass structures building line 100 comprises, for example:

-   -   a station configured to apply a liner;     -   a station configured to apply an under-liner;     -   at least one station configured to apply a carcass ply;     -   an optional station configured to apply metallic and/or textile         reinforcements;     -   an optional station configured to apply under-belt inserts.

The carcass structures building line 100 also comprises a second path 130 comprising building devices configured to build on the forming drum 110 a second part of structural components of the carcass structure.

The second path 130 of the carcass structures building line 100 comprises, for example:

-   -   a station configured to apply anti-abrasion inserts by wrapping         in a spiral a continuous elongated element around the first         stage forming drum 110;     -   an optional station configured to apply at least one portion of         sidewalls by wrapping in a spiral a continuous elongated element         around the forming drum 110.

Preferably, the first path 120 of the carcass structures building line 100 is substantially rectilinear.

Preferably, the second path 130 of the carcass structures building line 100 is substantially rectilinear and perpendicular to the first path 120.

In a corner area between the first path 120 and the second path 130 of the carcass structures building line 100 a working station 125 configured to form the beads of the tyre is arranged.

The carcass structures building line 100 also comprises a first transfer device 121 configured to transfer the forming drum 110 from the first path 120 to the beads formation station 125 and a second transfer device 122 configured to transfer the forming drum 110 from the beads formation station 125 to the second path 130.

Each of such transfer devices 121, 122 can comprise an anthropomorphous robot (for example a robotized arm having at least 6 movement axes) or a non-anthropomorphous Cartesian movement device, which allows movements according to three Cartesian axes X, Y, Z and, preferably, rotation around at least one, more preferably two of said Cartesian axes X and Y. The axes X and Y are indicated in FIG. 2 , the axis Z being perpendicular to the axes X and Y.

Preferably, each forming drum 110 can be moved among the various working stations of the carcass structures building line 100 in a sequence which is the same as or different from the spatial sequence of such working station.

Preferably, each forming drum 110 is moved by a trolley (not shown) along the first path 120 of the carcass structures building line 100. The trolley is preferably capable of moving, driven by a suitable motor, along suitable guides (preferably rectilinear) in two opposite directions of travel.

The building of the first part of components of the carcass structure is preferably carried out along the first path 120 of the carcass structures building line 100 while the forming drum 110 is associated with a pair of axially opposite support rings (not shown).

The forming drum 110 is dissociated from the aforementioned pair of support rings in the beads formation station 125 and along the second path 130 of the carcass structures building line 100.

The crown structures building line 200 comprises a first path 220 comprising building devices configured to build on the forming drum 210 a first part of structural components of the crown structure. The first path 220 of the crown structures building line 200 comprises, for example:

-   -   an optional station configured to apply under-belt inserts (such         a station is provided unless it is already comprised in the         first path 120 of the carcass structures building line 100);     -   at least one belt assembly building station;     -   an optional station configured to apply an under-layer.

The crown structures building line 200 also comprises a second path 230 comprising building devices configured to build a second part of structural components of the crown structure.

The second path 230 of the crown structures building line 200 comprises for example:

-   -   at least one station configured to apply a tread band by         wrapping in a spiral a continuous elongated element around the         forming drum 210;     -   an optional station configured to apply at least one portion of         sidewalls by wrapping in a spiral a continuous elongated element         around the forming drum 210. This last station is at least         provided either in said second path 130 of the carcass         structures building line 100 or in said second path 230 of the         crown structures building line 200.

The crown structures building line 200 also comprises a drum transfer device 221 configured to transfer the forming drum 210 from the first path 220 to the second path 230.

The drum transfer device 221 can comprise an anthropomorphous robot (for example a robotized arm with at least 6 movement axes) or a non-anthropomorphous Cartesian movement device, which allows movements according to three Cartesian axes X, Y, Z and, preferably, rotation around at least one, more preferably two of said Cartesian axes X and Y.

Preferably, each forming drum 210 can be moved among the various working stations of the crown structures building line 200 in a sequence which is the same as or different from the spatial sequence of such working stations.

Preferably, the first path 220 of the crown structures building line 200 is substantially rectilinear.

More preferably, the first path 220 of the crown structures building line 200 is substantially parallel to the first path 120 of the carcass structures building line 100.

Preferably, the second path 230 of the crown structures building line 200 is substantially rectilinear and perpendicular to the first path 220.

The shaping and assembling machine 300 is configured to sequentially shape, one at a time, the carcass structures as they arrive from the carcass structures building line 100, and to assemble them to the respective crown structures as they arrive from the crown structures building line 200, so as to obtain respective green tyres 2′. In the specific example illustrated herein, the shaping and assembling machine 300 is configured to shape the carcass structures and to assemble them to the respective crown structures on a shaping drum 330. Therefore, it operates on carcass structures and crown structures which have been dissociated from the respective forming drums 110 and 210. Such forming drums 110 and 210 are moved to return to the respective storage areas 111 and 211.

The built green tyres 2′ which exit from the shaping and assembling machine 300 are transferred to the molding and vulcanization station 400 wherein a molding and vulcanization process configured to define the structure of the tyre according to a desired geometry and tread pattern is carried out, thus obtaining the finished tyres 2.

With reference to FIGS. 3-17 , the crown structures building line 200 comprises a belt assembly building device 201. Preferably, such a device 201 is arranged at the first path 220 of the crown structures building line 200.

The belt assembly building device 201 comprises a trolley 21 moveable on a substantially rectilinear track 21 a. The track 21 a is arranged so as to obtain a movement of the trolley 21 along a rectilinear direction of movement A, which is preferably parallel to the first path 220 of the crown structures building line 200, and along a direction of movement B opposite to the direction of movement A.

As described hereinafter, during the movement thereof the trolley 21 supports a substantially cylindrical forming drum 25 in order to build thereon a belt assembly or only part thereof, depending on whether a cylindrical shaping of the belt assembly has to be carried out (in which case the trolley 21 always supports only the substantially cylindrical forming drum 25) or a toroidal shaping of the belt assembly has to be carried out (in which case the trolley 21 supports the substantially cylindrical forming drum 25 for a first part of the belt assembly building process and the substantially toroidal forming drum 210 for the remaining part of the belt assembly building process).

The forming drums 25 and 210 are radially contractable/expandable. Both of them comprise a plurality of angular sectors that are radially moveable in a synchronous manner. The angular sectors of the forming drum 25 are shaped so as to provide the forming drum 25 with a substantially cylindrical geometry whatever the radial dimension thereof, whereas the angular sectors of the forming drums 210 are shaped so as to provide the forming drum 210 with a substantially toroidal geometry whatever the radial dimension thereof.

The belt assembly building device 201 comprises a first working area W1 arranged downstream of a starting position P0 of the trolley 21 with reference to the direction of movement A and a second working area W2 arranged downstream of the first working area W1 with reference to the direction of movement A. The starting position P0 can also be defined in the first working area W1.

The first working area W1 comprises a crossed belt structure building device 22. For this purpose, the first working area W1 comprises a first operative station W1 a comprising a deposition apparatus 22 a configured to deposit a first belt layer having a plurality of first reinforcing cords tilted with a first orientation and a second operating station W1 b arranged downstream of the first operative station W1 a with reference to the direction of movement A and comprising a deposition apparatus 22 b configured to deposit a second belt layer having a plurality of second reinforcing cords tilted with a crossed orientation with respect to the orientation of the aforementioned first cords.

The second working area W2 comprises a deposition device 23 configured to deposit a zero degrees belt layer.

The belt assembly building device 201 comprises, downstream of the second working area W2 with reference to the direction of movement A, a first service area S1.

The first service area S1 comprises an annular holding member 30, shown in greater detail in FIG. 18 .

The annular holding member 30 comprises a base block 31 and an annular body 32 fixedly associated with the base block 31.

The annular body 32 comprises a plurality of angular sectors 35 (eight in the specific example shown in FIG. 18 ) circumferentially adjacent to one another and radially moveable in a synchronous manner, preferably upon receipt of a suitable electrical or pneumatic command, between a radially outermost operating position and a radially innermost non-operating position. Due to the possibility of movement of the angular sectors 35 the annular holding member 30 is therefore radially contractable/expandable.

In FIG. 18 the angular sectors 35 are shown in their non-operating position. Such a non-operating position corresponds to the configuration of maximum radial contraction of the annular holding member 30.

With reference to FIGS. 3-17 , the belt assembly building device 201 also comprises, downstream of the first service area S1 with reference to the direction of movement A, a second service area S2.

Two support members 41 and 45 are provided in the second service area S2. The support member 41 is configured to support a first forming drum (for example the forming drum 25 shown in FIGS. 19 and 20 ), whereas the support member 45 is configured to support a second forming drum (for example the forming drum 210 shown in FIGS. 19 and 20 ).

In the particular embodiment shown in FIGS. 19 and 20 , the two support members 41, 45 are part of a single manipulator 40.

The manipulator 40 is irremovably arranged in the second service area S2, i.e. when it is used it always remains in the same position with respect to the ground.

The manipulator 40 comprises a base frame 40 a stably positioned on the ground and a moveable group 40 b rotatable with respect to the base frame 40 a about a rotation axis R which is oblique with respect to the ground. In particular, the rotation axis R is tilted by an angle equal to 45° with respect to the ground.

The moveable group 40 b is associated with a service surface 44 of the base frame 40 a. Such a service surface is tilted by an angle equal to 45° with respect to the ground.

The two support members 41, 45, are fixedly associated with the moveable group 40 b, so that the rotation of the moveable group 40 b with respect to the base frame 40 a about the rotation axis R causes the rotation of the support members 41, 45, about the rotation axis R. Such a rotation can be driven by a motor assembly not visible in the figures. The angle of rotation can be set as desired.

Each support member 41, 45 comprises a respective support arm 42, 46 and a respective mounting axis. When the support member 42, 46 supports a respective forming drum the mounting axis thereof coincides with the rotation axis of the respective forming drum.

The two support arms 42, 46 extend along directions substantially perpendicular to one another and are configured to support the forming drums so that the mounting axis of one of the two support members 41, 45 (and therefore the rotation axis of one of the two forming drums) is arranged along a substantially horizontal direction and the mounting axis of the other support member 41, 45 (and therefore the rotation axis of the other forming drum) is arranged along a substantially vertical direction.

In the operative configuration shown in FIG. 19 , the support arm 42 supports the substantially cylindrical forming drum 25 so that the support member 41 is in a loading/unloading position and the rotation axis of the forming drum 25 (and therefore the mounting axis of the support member 41) is arranged along a horizontal direction, whereas the support arm 46 supports the substantially toroidal forming drum 210 so that the support member 45 is in a waiting position and the rotation axis of the forming drum 210 (and therefore the mounting axis of the support member 45) is arranged along a vertical direction.

In the operative configuration shown in FIG. 20 , the moveable group 40 b has rotated by 180° about the rotation axis R. In this configuration the support members 41, 45 have swapped their position, so that the support arm 42 supports the substantially cylindrical forming drum 25 so that the support member 41 is in the aforementioned waiting position and the rotation axis of the forming drum 25 is arranged along the aforementioned vertical direction, whereas the support arm 46 supports the substantially toroidal forming drum 210 so that the support member 45 is in the aforementioned loading/unloading position and the rotation axis of the forming drum 210 is arranged along the aforementioned horizontal direction.

Each forming drum 25, 210 is supported by the respective support arm 42, 46 by a respective damping device 43, 47 capable of compensating for possible axial movements of the forming drum 25, 210.

Preferably, each damping device 43, 47 comprises a plurality of pneumatic cylinders, at least some of which are functionally independent from the others so as to allow a different degree of compensations depending on whether the forming drum 25, 210 is arranged with its rotation axis extending along a horizontal or vertical direction.

As already stated, the belt assembly building device 201 makes it possible to carry out both a cylindrical shaping of the belt assembly and a toroidal shaping of the belt assembly.

When a toroidal shaping of the belt assembly has to be carried out, the belt assembly building device 201 is configured to take the operative configuration shown in FIG. 3 , wherein the trolley 21 is in its starting position P0 (or in the first working area W1 in the case in which the starting position P0 is defined in the first working area W1) and supports a substantially cylindrical forming drum 25. In this operative configuration, the support arm 42 of the manipulator 40 is oriented so that the support member 41 is arranged in the aforementioned loading/unloading position (and therefore the mounting axis of the support member 41 is oriented along a horizontal direction), whereas the support arm 46 is oriented so that the support member 45 is arranged in the aforementioned waiting position (and therefore the mounting axis of the support member 45 is oriented along a vertical direction) and supports a substantially toroidal forming drum 210, as shown in FIG. 19 .

Thereafter, the trolley 21 with the forming drum 25 is moved along the direction of movement A until the forming drum 25 is brought to the first working area W1. Such movement is not actuated when the starting position PO is defined in the first working area W1.

As shown in FIG. 4 , the trolley 21 is stopped when the forming drum 25 is at the first operative station W1 a, where a first belt layer, like for example the belt layer 8 a of the tyre 2 of FIG. 1 , is deposited on the forming drum 25 by the deposition apparatus 22 a.

As shown in FIG. 5 , the trolley 21 is subsequently moved along the direction of movement A and stopped when the forming drum 25 is at the second operative station W1 b, where a second belt layer, like for example the belt layer 8 b of the tyre 2 of FIG. 1 , is deposited on the forming drum 25 by the deposition apparatus 22 b in a radially outer position with respect to the first belt layer, thus building on the forming drum 25 a crossed belt structure, like for example the crossed belt structure 8 of the tyre 2 of FIG. 1 .

As shown in FIG. 6 , the trolley 21 is subsequently moved along the direction of movement A and stopped when the forming drum 25, carrying the crossed belt structure, reaches the first service area S1 and is arranged in a radially inner position with respect to the annular holding member 30.

The crossed belt structure is then transferred from the forming drum 25 to the annular holding member 30. Such transferal comprises at first the radial contraction of the annular holding member 30 through a synchronous radial movement of the angular sectors 35 until the angular sectors 35 contact the crossed belt structure and, thereafter, the radial contraction of the forming drum 25 through a synchronous radial movement of the relative angular sectors.

At this point the crossed belt structure remains fixedly connected to the annular holding member 30 and the trolley 21 is moved along the direction of movement A to bring the forming drum 25, without the crossed belt structure thereon, to the second service area S2, where it is transferred to the first support member 41, as shown in FIG. 7 .

Thereafter, as shown in FIG. 8 , the trolley 21 is moved along the direction of movement B so as to move away from the second service area S2.

As shown in FIG. 9 , at this point the moveable group 40 b of the manipulator 40 is driven in rotation about the rotation axis R by an angle of 180°. Such a rotation causes a rotation of the support member 41 about the rotation axis R until it is brought to the waiting position originally occupied by the support member 45 and, simultaneously, a rotation of the support member 45 about the rotation axis R until it is brought to the loading/unloading position originally occupied by the support member 41. The forming drum 25 thus has its rotation axis oriented along a vertical direction and the forming drum 210 has its axis oriented along a horizontal direction, as shown in FIG. 20 .

Thereafter, as shown in FIG. 10 , the trolley 21 is moved along the direction of movement A so as to pick up the forming drum 210 from the support member 45.

Thereafter, as shown in FIG. 11 , the trolley 21 is moved along the direction of movement B until the forming drum 210 is arranged in the first service area S1, in a radially inner position with respect to the annular holding member 30.

The crossed belt structure is then transferred from the annular holding member 30 to the forming drum 210. Such a transfer comprises the radial expansion of the forming drum 210 through a synchronous radial movement of its angular sectors until such angular sectors bring the forming drum 210 to take an expanded condition in which the aforementioned angular sectors are in contact with the crossed belt structure supported by the annular holding member 30. In order to facilitate the aforementioned transfer it is a radial expansion of the annular holding member 30 can be provided when the forming drum 210 has taken to the aforementioned expanded condition. The radial expansion of the annular holding member 30 can also be at least in part simultaneous with the radial expansion of the forming drum 210.

Preferably, the forming drum 210 remains in the aforementioned expanded condition up to the end of the crown structure building cycle.

Once the crossed belt structure has been transferred to the forming drum 210, as shown in FIG. 12 , the trolley 21 is moved along the direction of movement B to bring the forming drum 210, with the crossed belt structure thereon, to the second working area W2, where the zero degrees belt layer, like for example the zero degrees belt layer 8 c of the tyre 2 of FIG. 1 , is deposited on the forming drum 210, in a radially outer position with respect to the crossed belt structure. In this way, the desired toroidal shaping of the belt assembly, like for example the belt assembly 8′ of the tyre 2 of FIG. 1 , is obtained.

Thereafter, as shown in FIG. 13 , the trolley 21 is moved along the direction of movement A to bring the forming drum 210, with the belt assembly thus formed thereon, to the second service area S2, where it is transferred to the second support member 45.

The trolley 21 is subsequently moved along the direction of movement B so as to move away from the second service area S2, as shown in FIG. 14 .

As shown in FIG. 15 , at this point the moveable group 40 b of the manipulator 40 is driven in rotation about the rotation axis R by an angle of 180°. Such a rotation causes a rotation of the support member 45 about the rotation axis R until it is brought to the waiting position previously occupied by the support member 41 and, simultaneously, a rotation of the support member 41 about the rotation axis R until it is brought to the loading/unloading position previously occupied by the support member 45. The forming drum 210 thus has its rotation axis oriented along a vertical direction and the forming drum 25 has its axis oriented along a horizontal direction, as shown in FIG. 19 .

Thereafter, as shown in FIG. 16 , the trolley 21 is moved along the direction of movement A so as to pick up the forming drum 25 from the support member 41.

Thereafter, as shown in FIG. 17 , the trolley 21 with the forming drum 25 is moved along the direction of movement B until it goes back to its starting position PO (or to the first working area W1 in the case in which the starting position PO is defined in the first working area W1). During such a movement the forming drum 25 passes in a radially inner position with respect to the annular holding member 30 without stopping in the first service area S1, in the second working area W2 and, in the case in which the starting position PO is not defined in the first working area W1, in such a first working area W1.

Shortly before, or during or just after the movement of the trolley 21 to bring the forming drum 25 from the second service area S2 to the starting position P0 (or to the first working area W1 in the case in which the starting position P0 is defined in the first working area W1), the drum transfer device 221, shown in FIG. 2 , picks up the forming drum 210 from the support member 45 to send it to the path 230 of the crown structures building line 200 and a new substantially toroidal forming drum 210′, shown in FIG. 17 , is arranged on the support member 45, preferably again by the drum transfer device 221.

The building device 201 of the belt assembly described above can thus proceed with a new building cycle of a belt assembly having a toroidal shaping, repeating the actions described above.

From the above description it is clear that in a normal operation of the plant of FIG. 2 a plurality of substantially toroidal forming drums 210, 210′ enter into/exit from the belt assembly building device 201 in succession, whereas the forming drum 25 always remains inside such a building device 201.

Preferably, in the plant of FIG. 2 there are 5 or 6 substantially toroidal forming drums that circulate simultaneously in the crown structures building line 200.

Such forming drums have diameters, in the contracted configuration thereof, preferably comprised between 500 mm and 900 mm and allow a maximum radial expansion equal to 300 mm. Consequently, the annular holding member 30 must also be able to have a similar radial expansion.

When a cylindrical shaping of the belt assembly has to be carried out, the building device 201 of the belt assembly is configured to take an operating configuration that differs from the one shown in FIG. 3 only in that the support member 45 also supports a substantially cylindrical forming drum, hereinafter indicated as second substantially cylindrical forming drum, which is totally equivalent to the substantially cylindrical forming drum 25 described earlier.

Thereafter, the trolley 21 with the forming drum 25 is moved along the direction of movement A until the forming drum 25 is brought into the first working area W1.

In an analogous manner to what is shown in FIG. 4 , the trolley 21 is stopped when the forming drum 25 is located at the first operative station W1 a, where the first belt layer is deposited on the forming drum 25 by the deposition apparatus 22 a.

In an analogous way to what is shown in FIG. 5 , the trolley 21 is subsequently moved along the direction of movement A and stopped when the forming drum 25 is at the second operative station W1 b, where the second belt layer is deposited on the forming drum 25 by the deposition apparatus 22 b, in a radially outer position with respect to the first belt layer, thus building on the forming drum 25 the crossed belt structure.

Thereafter, the trolley 21 is subsequently moved along the direction of movement A and stopped when the forming drum 25 reaches the second working area W2, where the zero degrees belt layer is deposited on the forming drum 25 by the deposition device 23, in a radially outer position with respect to the crossed belt structure, thus obtaining the desired cylindrical shaping of the belt assembly.

Thereafter, the trolley 21 is moved along the direction of movement A until the forming drum 25, after having crossed the first service area S1, without stopping there and passing in a radially inner position with respect to the annular holding member 30, reaches the second service area S2, where it is transferred to the support member 41.

Thereafter, the trolley 21 is moved along the direction of movement B so as to move away from the second service area S2.

At this point the moveable group 40 b of the manipulator 40 is driven in rotation about the rotation axis R by an angle of 180°. Such a rotation brings the forming drum 25 to the position originally occupied by the second substantially cylindrical forming drum and the latter to the position originally occupied by the forming drum 25. The forming drum 25 thus has its rotation axis oriented along a vertical direction and the second substantially cylindrical forming drum has its axis oriented along a horizontal direction.

Thereafter, the trolley 21 is moved along the direction of movement A so as to pick up the second substantially cylindrical forming drum from the support member 45.

Thereafter, the trolley 21 with the second substantially cylindrical forming drum is moved along the direction of movement B until it goes back to its starting position P0 (or to the first working area W1 in the case in which the starting position P0 is defined in the first working area W1). During such movement the second substantially cylindrical forming drum passes in a radially inner position with respect to the annular holding member 30 without stopping in the first service area S1, in the second working area W2 and in the first working area W1.

Shortly before, or during or just after the movement of the trolley 21 to bring the second substantially cylindrical forming drum from the second service area S2 to the starting position PO (or to the first working area W1 in the case in which the starting position PO is defined in the first working area W1), the drum transfer device 221, shown in FIG. 2 , picks up the forming drum 25 from the support member 41 to send it to the path 230 of the crown structures building line 200 and on the support member 41 is arranged, preferably again by the drum transfer device 221, a further substantially cylindrical forming drum, also totally equivalent to the substantially cylindrical forming drum 25 described earlier, in the case in which a cylindrical shaping of a new belt assembly has to be carried out, or a substantially toroidal forming drum, like for example the forming drum 210, 210′ shown in FIGS. 3-17 , in the case in which a toroidal shaping of the belt assembly has to be carried out.

The present invention has been described with reference to some preferred embodiments. Different modifications can be made to the embodiments described above, while remaining within the scope of protection of the invention defined by the following claims. 

1. A process for producing tyres for vehicle wheels, comprising building a crown structure of the tyre, wherein building said crown structure comprises: building a crossed belt structure on a substantially cylindrical first forming drum; transferring said crossed belt structure from said first forming drum to an annular holding member; arranging a radially contractable/expandable second forming drum in a radially inner position with respect to said annular holding member; transferring said crossed belt structure from said annular holding member to said second forming drum by radially expanding said second forming drum until it-said second forming drum is brought into an expanded condition in which said second forming drum is in contact with said crossed belt structure so as to toroidally shape said crossed belt structure; and depositing at least one zero degrees belt layer on said second forming drum in a radially outer position with respect to said toroidally-shaped crossed belt structure.
 2. The process according to claim 1, wherein building said crossed belt structure comprises: arranging said first forming drum in a first working area; and depositing at least one belt layer on said first forming drum in said first working area.
 3. The process according to claim 2, wherein i) the arranging said first forming drum in a first working area comprises—arranging said first forming drum in a first operative station defined in said first working area; and ii) the depositing at least one belt layer on said first forming drum in said first working area comprises: depositing a first belt layer on said first forming drum in said first operative station; moving said first forming drum along a first direction of movement from said first operative station to a second operative station defined in said first working area downstream of said first operative station with reference to said first direction of movement; and depositing a second belt layer on said first forming drum in a radially outer position with respect to said first belt layer in said second operative station.
 4. The process according to claim 3, wherein the transferring said crossed belt structure from said first forming drum to said annular holding member comprises: moving said first forming drum along a first direction of movement from said first working area to a first service area arranged downstream of said first working area with respect to said first direction of movement and comprising said annular holding member; and arranging said first forming drum in a radially inner position with respect to said annular holding member.
 5. The process according to claim 4, wherein said first forming drum and said annular holding member are radially contractable/expandable and wherein the transferring said crossed belt structure from said first forming drum to said annular holding member further comprises, after having arranged said first forming drum in a radially inner position with respect to said annular holding member: radially contracting said annular holding member until said annular holding member is brought into contact with said crossed belt structure; and radially contracting said first forming drum leaving said crossed belt structure associated with said annular holding member.
 6. The process according to claim 5, wherein building said crown structure comprises, after having transferred said crossed belt structure from said first forming drum to said annular holding member: moving said first forming drum along said first direction of movement from said first service area to a second service area arranged downstream of said first service area with respect to said first direction of movement and comprising a first support member; and transferring said first forming drum to said first support member.
 7. The process according to claim 6, wherein said first support member is moveable in said second service area between a first loading/unloading position and a waiting position and wherein the transfer of said first forming drum to said first support member is performed when said first support member is in said first loading/unloading position.
 8. The process according to claim 7, wherein arranging said second forming drum in a radially inner position with respect to said annular holding member comprises: moving said second forming drum from said second service area to said first service area along a second direction of movement opposite to said first direction of movement.
 9. The process according to claim 8, wherein said second service area comprises a second support member that supports said second forming drum before said second forming drum is moved from said second service area to said first service area, said second support member being moveable in said second service area between a second loading/unloading position and a third loading/unloading position, and wherein building said crown structure comprises, before moving said second forming drum from said second service area to said first service area, moving said second support member from said second loading/unloading position to said third loading/unloading position.
 10. The process according to claim 9, wherein moving the first forming drum between said first loading/unloading position and said waiting position is performed simultaneously with moving the second forming drum between said second loading/unloading position and said third loading/unloading position.
 11. The process according to claim 10, wherein said third loading/unloading position coincides with said first loading/unloading position and said waiting position coincides with said second loading/unloading position.
 12. The process according to claim 11, wherein depositing said at least one zero degrees belt layer on said second forming drum comprises, after having transferred said crossed belt structure from said annular holding member to said second forming drum in said first service area; moving said second forming drum along said second direction of movement from said first service area to a second working area arranged between said first working area and said first service area.
 13. The process according to claim 12, wherein building said crown structure comprises, after having deposited said at least one zero degrees belt layer on said second forming drum in said second working area: moving said second forming drum from said second working area to said second service area along said first direction of movement; and transferring said second forming drum to said second support member.
 14. The process according to claim 13, wherein building said crossed belt structure comprises, after having transferred said second forming drum to said second support member: moving said first forming drum from said second service area to said first working area along said second direction of movement.
 15. The process according to claim 14, wherein building said crown structure comprises, after having transferred said second forming drum to said second support member: picking up said second forming drum from said second support member by a drum transfer device; and associating a third substantially toroidal forming drum with said second support member.
 16. A plant for producing tyres for vehicle wheels, comprising a building line configured to build a crown structure, wherein said building line comprises a building device configured to build a belt assembly, wherein said building device comprises: a trolley moveable along a first direction of movement; a substantially cylindrical first forming drum configured to be coupled with said trolley; a contractable/expandable second forming drum configured to take-assume a substantially toroidal shaping and configured to be coupled with said trolley; a first working area comprising a building device configured to build a crossed belt structure; a second working area arranged downstream of said first working area with respect to said first direction of movement and comprising a depositing device configured to deposit at least one zero degrees belt layer in a radially outer position with respect to said crossed belt structure; a first service area arranged downstream of said second working area with respect to said first direction of movement and comprising an annular holding member; and a second service area arranged downstream of said first service area with respect to said first direction of movement.
 17. The plant according to claim 16, wherein said building device configured to build the crossed belt structure comprises: a first depositing apparatus configured to deposit a first belt layer, said first depositing apparatus being arranged in a first operative station defined in said first working area; and a second depositing apparatus configured to deposit a second belt layer, said second depositing apparatus being arranged in a second operative station defined in said first working area downstream of said first operative station with respect to said first direction of movement.
 18. The plant according to claim 17, wherein said first forming drum is radially contractable/expandable.
 19. The plant according to claim 18, wherein said annular holding member is radially contractable/expandable.
 20. The plant according to claim 19, wherein said second service area comprises a first support member configured to support said first forming drum.
 21. The plant according to claim 20, wherein said second service area comprises a second support member configured to support said second forming drum.
 22. The plant according to claim 21, wherein said first support member and said second support member are associated with a single manipulator irremovably arranged in said second service area.
 23. The plant according to claim 22, wherein said manipulator is a rotating manipulator with an oblique rotation axis.
 24. The plant according to claim 23, wherein said first forming drum is moveable by said trolley from said second service area to said first working area along said second direction of movement passing in a radially inner position with respect to said annular holding member without stopping in said first service area and in said second working area.
 25. The plant according to claim 24, wherein said second forming drum is moveable from said second working area to said second service area along said first direction of movement passing in a radially inner position with respect to said annular holding member.
 26. The plant according to claim 25, wherein a plurality of substantially toroidal forming drums enter into, and exit from, said building device configured to build the belt assembly in succession whereas said first forming drum always remains inside said building device. 